1. Field of the Invention
The present invention relates generally to tillage equipment, and in particular, to agricultural implements having first and second gangs of rotatable tillage tools arranged to follow each other along a line of travel.
2. Description of the Related Art
Conventional tandem X-shaped disk harrows use a forward swept front gang configuration where the front disk blades throw the soil outward from the center, resulting in a downward and inward set of blade reaction forces to acquire higher soil penetration loads than the machine could generate by its own weight. This system worked well for early general purpose disk harrows where the common disk blade diameter was 18″ to 22″ and machine frames generating less than 150 pounds per blade.
With the increase in crop residue and the need for greater soil penetration over the years, today's general purpose disk harrows now use 24″ diameter blades with machine frames generating 200 plus pounds per blade. Consequently, with the added machine weight and increased horsepower of today's tractors, the forward swept gang configuration can generate unstable reaction forces at the wing hinge points that may result in frame buckling, outer end soil ridging, unlevel field performance and high speed frame bounce. To help stabilize the front wing gangs, wing gauge wheel assemblies have been added by manufactures to dampen and prevent excessive unstable blade reaction forces. For proper machine operation, the gauge wheel assemblies require constant adjustments for different soil conditions and different machine operating depths. High speed frame bounce is usually caused by the harmonic action between the front gang's C-shank spring hangers and a very firm soil profile at speeds above 7 mph. The forward swept wing gangs bite into the firm soil compressing the spring hangers which then recoil upward to allow the gangs to raise up slightly. The gangs bite in again and recoil a little higher, over and over until the frame takes on a noticeable bounce as it traverses the field.
There is a need for a better gang configuration that provides stable reaction forces to prevent wing buckling and high speed frame bounce while eliminating the need for front wing gauge wheels. An inverted front V-shaped gang with its apex pointed in the direction of travel has been used successfully on a disk harrow frame for many years. Sometimes referred to as a “diamond disk,” they have some advantages and disadvantages over the conventional X-shaped disk harrows. One advantage is the ability to operate in floating hitch mode due to the stable, self-gauging nature of the front gangs. The blade reaction forces on an inverted front gang are outward instead of inward, providing stable tension across the front hinge line. Floating hitch operation mode provides better disk harrow performance on fields with widely varying terrain changes or rocky fields that need gang protection. Under different field conditions, such as shallow seedbed preparation on low sloped fields, the same tillage tool may work better in a more traditional spring-biased hitch operation mode.
Another advantage of an inverted front gang arrangement is the ability to maintain level field performance over a wide variety of operating depths, operating speeds and gang angle changes. The level performance of an X-shaped disk harrow is very sensitive to any type of dynamic gang force changes, resulting in the need to continually re-adjust the front-to-rear level settings and/or front wing gauge wheel position. An inverted front gang arrangement with stable blade reactions, can handle wide variations in dynamic gang force changes without the need for continuous level adjustments.
There are two main disadvantages of an inverted front gang arrangement over conventional X-shaped disk harrows. The weight distribution between the center frame and the wing frames are polar opposites between the two different gang arrangements. The X-shaped disk harrow has a short front-to-rear dimension for its center frame, and wing frames that are generally longer than the center frame. The longer wing frames help distribute the needed weight to the wings to balance out the average weight per blade.
In contrast, the diamond-shaped disk harrow has a long front-to-rear center frame dimension, and wing frames that are generally shorter than the center frame. The center frame weight per blade will likely be much higher than the weight per blade of the wings causing the wings to not penetrate as well as the center frame. Ideally, in order to balance the weight per blade by physical weight alone, weight would need to be added to the wing sections along with some reduction in weight from the center frame. By adding physical weight to the wings, the folded transport center of gravity will rise causing possible unsafe conditions on roadside inclines.
Another disadvantage of a symmetrical diamond-shaped gang arrangement is the front center soil movement being thrown into each other causing plugging and/or not tilling the center line area. If the spacing between the front left and right gangs is widened to prevent plugging, larger weeds at the center line will not be removed.
There is a need for an improved frame and gang arrangement that eliminates these disadvantages while adding diverse gang angle and hitch operation modes, in an efficient compact economical design.